Loop antenna



April 1947- H. G. BUSlGNlES ETAL 2,419,673

LOOP ANTENNA Filed March 5, 1945 5 Sheets-Sheet l April 29, 1947- H. s. suslcmn-zs ETAL 2,419,673

LOOP KNTENNA I Filed March 5, 1943 5 Sheets-Sheet 2 April 1947- H, G. BUSIGNIES ETAL 2,419,673

' LOOP ANTENNA Filed March 5, 1943 5 Sheets-Sheet 3 w: s M g;

M i INVENTORVJ.

April 1947- H. G. BUSIGNIES EIAL 2,419,673

LOOP ANTENNA Filed March 5, 1945 5 Sheets-Sheet 4 April 29, 1947. BuslGNEs ETAL' 2,419,673

LOOP ANTENNA Filed March 5, 1943 5 Shets-Sheet 5 Patented Apr. 29, 1947 UNITED STATES PATENT OFFICE LOOP ANTENNA Application March 5, 1943, Serial No. 478,083

8 Claims. 1

This invention relates to improvements in loop antennas, and more particularly to loop antennas made from a shielded flexible cable.

An object of this invention is to provide a simple but strong and rigid loop antenna.

Another object of this invention is to provide a shielded loop antenna structure utilizing shielded cable.

Other objects and advantages of the present invention will become apparent from the following description of a preferred embodiment thereof, illustrated in the accompanying drawings wherein:

Fig. l is a vertical View partly in section, of the general antenna assembly in accordance with the present invention;

Fig. 2 is a top plan view of the general antenna assembly illustrated in Fig. 1;

Fig. 3 is an enlarged cross-sectional view of the upper portion of the loop antenna assembly;

Fig. 4 is an enlarged cross-sectional view of an adjustable loop support;

Fig. 5 is an enlarged cross-sectional View of a base for the antenna assembly;

Fig. 6 is an enlarged cross-sectional View of a preferred form of cable to be used for the loop.

An application of the use of flexible cable to form a loop antenna is generally illustrated by way of example in Figs. 1 and 2 in connection with a loop antenna, sense antenna and counterpoise arrangement more fully described in the co-pending applications of T. H. Clark, S N. 478,081, filed March 5, 1943, T. H. Clark- P. J. Vander Woude, S. N. 478,082, filed March 5, 1943. This antenna assembly may include a generally vertical supporting rod Iii from the midpoint of which extend four radial arms i2 spaced 90 relatively to one another and attached to the rod it by means of a suitable connector 13. The bottom of the supporting rod IE] is held in a strengthening support M which, in turn, is mounted upon a generally hemispherical base member it. The latter, in turn, may be attached to the top of a ship mast indicated at H. The four arms 22 may be interconnected by bracing bars 23 attached thereto by suitable clamping devices 22.

The crossed loop in accordance with the present invention is formed by two flexible shielded cables i i and the tops of which pass through a top mount it, attached to the top of a supporting rod Hi, the ends of which are fastened at the base member it, and the central portions of which are held by fastening devices 28 on the ends of the respective arms !2. Above the top mount 18 is fixed an insulating ring 29 which supports a metal cap 30 from which projects a plurality of counterpoise rods 32. These rods are spaced at 90 relatively to one another and, in accordance with the 5 disclosure of the afore-mentioned T. H. Clark application, they may extend in a direction to bisect the angle between the crossed loops. A sense antenna 34 extends upwardly from an insulating disk 38 mounted on top of the cap 30.

The upper portion of the loop, and more particularly the manner in which it is fastened to the top mount 30 is more fully illustrated in Fig. 3. It will be seen from Figs. 1 and 3 that the top of the supporting rod I0 is provided with a flange 33, While the lower portion of the top mount I8 is provided with a comparable flange 40, adapted to be connected to the flange 38. An insulating lll'lg 29 is attached to the top mount [8 by means such as bolts 44, while the cap 30 is mounted upon the ring 29 by similar means such as bolts 46.

The tops of the cables forming the two loops pass, as illustrated, through the top mount l8. In order to securely hold the loops in place and prevent a strain upon the top curved portions, the loops are securely held in openings in this top mount. For this purpose the openings in the top mount I8 may be provided with a rubber or other insulating bushing 62 through which is passed a metal sleeve 66 which, inturn, encloses a rubber sleeve 64 immediately surrounding and attached to be pressed against the cable 24. The sleeve 66 is formed with a collar 68 on one end, which presses against the inner end of the bushing 62, limiting movement of the sleeve 65 in the downward direction, and is threaded on its outer end. A cap ll screws over the threaded end of the sleeve 66 and, through a metal Washer 14 presses tightly against the rubber sleeve 64, squeezed down upon the surface of the cable. As previously stated, in accordance with the present invention, each loop is formed from a flexible shielded cable, the shield being formed by an outer steel braid l0. This steel braid is out ofi just above the collar 68 and a ferrule 12 brazed to the braid, this ferrule projecting over the end of the collar 68 and assisting in preventing downward strain upon the cable.

As is common practice in shielded loop construction, the upper portion of each loop will be unshielded so that by removal of the braid l0 and any inner braid, if used, the top of each loop will consist solely of insulated conductor 18. In Fig. 3 there may also be seen the end of the cable 26 which may pass over (or beneath) the unshielded portion 18 of the cable 24. In order to properly 55 attach the cable holding means in the top mount and to firmly make connections Within this top mount, the latter may be in a somewhat skeletonized form, being provided with a plurality of through working apertures 11.

In order to properly tension the flexible cable without, at the same time preventing strain upon the bends of the cable, we provide a special supporting bracket 28 on the ends of the cross arms I2. This bracket is illustrated in more detail in Fig. 4, and will be seen to have a generally Y- shape, the arms of the Y in this case lying in a generally vertical plane. The clamping means themselves may consist of half shell clamping sections 280, enclosing a rubber bushing 202 which closely surrounds straight portions of the loop and which is held to the bracket 28 by these clamping shields. The latter may be attached to the bracket proper by means such as screws 204. Ferrules 206 are soldered or brazed to the outer shield 18 on the cable 24, these ferrules being attached at the end of the curved portion of the loop to prevent strain upon such curved portion resulting from tension on the straight portions.

In order to tension the loop as a whole to form a rigid loop structure, means are provided for adjusting the position of the bracket 28 upon the end of the crossed arms I2. For this purpose the crossed arms I2 are preferably made hollow and in their hollow ends are mounted insulators 288 provided with two reduced sections, one having a pin opening 2I0 and adapted to fit into the end of the cross arm and the other having a pin opening 2l2 adapted to fit into sleeve 2I4. Pins through the openings 2 I and 2 I2 will respectively attach the insulator 208 to the cross arm I2 and the bracket 28, while at the same time separating these two parts. The sleeve 2| 4 is adapted to be slidably mounted within a bore 2| 6 in the bracket 28, relative rotation being prevented by a suitable keyway 2 I8 in cooperation with adjustable key-engaging members 226. In accordance with the present invention one end of the sleeve 2I4 is closed but is provided with a threaded opening into which projects the end of a threaded shaft 222. On this shaft is a collar 226 which rests against a shoulder 228 of the bore 2I6. An extension 230 on the shaft 222 projects outwardly from the bracket 28 and is suitably shaped so that it may be engaged by an adjusting tool (not shown). The operation of the adjusting arrangement illustrated in Fig. 4 will be clear to those skilled in this art. Rotation of the shaft 222 will, through its reaction on sleeve 2I4 move the bracket inwardly or outwardly, as desired, and will thus control the tension of the straight portions or" the loops between the brackets and the top mount on the base. The straight portions of the loop may in this arrangement be made extremely rigid so that there will be no variations in the loop to effect the calculations of the direction finding system as a whole, while at the same time there will be no strain upon the curved portions of the loop since the tensioning points are formed by the clamp 200 on either side of said curved portion. It will be noted in this connection that the same condition holds true for the connection of the top of the loop in the top mount, which is due to the rigid connecting device illustrated. The strain caused by tensioning of the cable from the adjustable bracket 28 will be upon the connecting device at the top of the loop and not upon the top of the loop itself.

In Fig. we have illustrated some details of a base member upon which the loop antenna or the line antenna assembly may be mounted. This may consist of a generally hemispherical hollow casting I6 which will rest upon a suitable flange I38 on top of the mast I1. The seating gasket I39 is interposed between the castings I6 and the flange I38, and a tight connection may be made through means such as bolts MI. The sloping side of the castings I6 are formed by four spaced openings I44 to receive the ends of the loops 24 and 26. These loop ends must be rigidly attached to the base together to the loop structure and the connection may also be made water-tight. In accordance with the present invention, it is also made rigid; to eifect such an arrangement, the openings I44 are provided on the outside with a circular internally threaded portion adapted to receive a collar I50 externally threaded at both ends. One end of the collar I50 is threaded into the openings I44 and presses against a grounding washer I48 which, in turn, presses against the end of a ferrule I48 brazed or otherwise attached to the braided shield 10 on the cable 24. Within the collar I50 is spaced a rubber sleeve i52 which tightly grips the surface of the cable and is pressed against the cable and externally against the collar I 50 by means of a compression nut I54 threaded over the other end of the collar. This arrangement holds the cables tightly with respect to the base I5. but leaves the two ends of the loops free of strain so that they may be connected to appropriate terminal blocks I56. Similar holding means are, of course, used to hold the lower ends of the loop 25.

These terminal blocks I56 are preferably positioned around the bottom of the base I6 and are mounted in suitable openings therein and attached thereto by means such as screws I58 and I60. On the inner side of the terminal blocks I56 and held in place between another upon the screws I 58 are clamps I82 which surround the shielded ends of the cable and rigidly hold them to the terminal block. Leads I64 extend from each screw I58 to a common central rod I66 passing from one side toward terminal block through to the other. A lead I68 on the outside of the terminal block connects the pin I66 to the shield I10 of a flexible cable I12 extending down and externally of the mast I1 to the radio equipment. The terminal blocks I56 are also provided with a pair of pins I14 to which are attached the ends of the loop conductors themselves. Between the pins H4 and a second pair of pins I18 positioned immediately below them are attached resistors I16 for the purpose of improving characteristics of the loop antenna as more clearly explained in a copending application of Daubaras, S. N. 478,079, filed March 5, 1943. The lower pins I18, in turn, are attached through leads I to the dual wires of the cable I12. The various pins I86, H4 and I18 may be held in place in the terminal blocks by enlarged fluted portions I81. The details of this base structure are also more clearly explained and claimed in the aforementioned Clark-Vander- Woude application.

The dual cables I12 formin th transmission line to the radio apparatus are held within the base I6 by means of rubber bushings I86 pressed about the end thereof and mounted on one side in a cup-shaped rubber I84 of each terminal block and held on the outside by covers I90 which are attached about the openings in the base I6 as by bolts I92. These covers at the same time serve to protect the outer sides of the terminal blocks and in order to provide a water-tight connection suitable gaskets we may be interposed between each cover and the base.

The type of cable which has been used, by way of example, to form the shielded loop of the present invention is illustrated in cross-section in Fig. 6. As is there illustrated, such cable will preferably consist of an inner conductor 25!] surrounded by two lines of insulation 252 and 254. About these two lines of insulation is a copper braid 256 which, in turn, is surrounded by another line of insulation 258. A steel braid l0 surrounds the entire cable and forms the shield thereof. While this form of cable has proven to be particularly adaptable for use to form a shielded loop antenna, it is to be clearly under stood, of course, that the invention contemplates using any comparable shielded insulated flexible cable.

For the sake of clarity, the invention has been described in connection with certain specific apparatus, more particularly certain direction finding equipment but, it is to be understood that the particular structural details given have been presented by way of example and that the invention is not to be considered as limited thereto but only as set forth in the objects and the following claims.

We claim:

1. A loop antenna including, in combination, a framework having a base, a central vertical supporting rod projecting therefrom, cross arms extending radially outwardly from said vertical rod, and a shielded flexible cable attached at its top to the top of said rod, stretched over the ends of said cross arms and having its ends fixed to said base member.

2. The combination according to claim 1, in combination with spaced means on the top of said rod, firmly gripping the cable on either side of the top of said cable, and spaced means on the end of each cross arm, gripping the cable at two spaced points at either side of the corners of said cable, whereby said cable is firmly held in place without strain on its bent sections.

3. The combination according to claim 1, in combination with a Y-shaped bracket on the end of each cross arm, and clamping means on the ends of the arms of each Y for gripping said cable to hold the same rigidly relative to the top of the supporting rod and to said base member respectively, without strain on that portion of the cable between the arms of each Y.

4. The combination according to claim 1, in combination with cable clamping means on the outer end of each cross arm, and means for radially adjusting the position of said clamping means.

5. A loop antenna including in combination, a framework having a base, a central vertical supporting rod projecting therefrom, cross arm extending radially outwardly from said vertical rod, a shielded flexible cable attached at its top to the top of said rod, stretched over the ends of said cross arms and having its ends fixed to said base member, a Y-shaped bracket on the end of each cross arm, means for radially adjusting each Y-shaped bracket, and clamping means on the ends of the arms of each Y for gripping the cable.

6. The combination according to claim 5, in combination with a pair of ferrules firmly attached to the shielding on that portion of said cable extending between the arms of the Y of each bracket and bearing against said clamping means.

7. The combination according to claim 5, in which said clamping means each include a rubber bushing tightly engagin the outer surface of the cable, and means for attaching said rubber bushings to the arms of each Y-shaped bracket.

8. The combination according to claim 5, in which each Y-shaped bracket is formed with a hollow bore in its base, in combination with an extension on each cross arm projecting into said bore, and in which said adjusting means includes a threaded shaft in said bore threadably engaging the extension on each cross arm, a collar on said shaft bearing against the end of said bore, and an extension on said shaft projecting from the base of said bracket and adapted to be turned for rotating said threaded shaft and varying the relative position of the bracket on the cross arm.

HENRI G. BUSIGNIES. PHILIP J. VANDER WOUDE. 

